It is often necessary to provide a flow of powdered bulk material to processing machinery or analyzing equipment. Feeders are used for controlling the input of bulk materials in operations such as packaging, batching, grinding, weighing, flaking, freezing, drying and mixing. Sometimes, the accurate feeding of these particles is negatively affected by the properties of the powder being fed into the system.
The powder can have a wide particle size distribution and the larger particles can mask the presence of of smaller particles during analysis. Fine powders can cluster into larger particles because of static charges. The particle morphology can tend to allow the particles to interlock mechanically to form larger clumps. Furthermore, some powders consist of large particles with small satellite particles adhering to the surface. One common prior art method of dispersing the powdered material is to place the material in a vibratory tray to dislodge and transport the powder. These "vibratory feeders" are manufactured by a number of companies, including FMC Corporation of Homer City, Pa. The powder-filled tray or trough, mounted on flexible springs, is vibrated at a high speed (30-60 Hz) by an electromagnetic drive.
These prior art vibratory dispersers have a number of problems in some applications, especially when processing fine layers or small quantities of powder. Often the mechanical forces created in the vibratory dispersers are not sufficient to disloge clumped powder. Furthermore, the vibratory dispersers can actual increase the clustering of material due to static charges.
It is thus an object of the invention to provide a powder disperser which can quickly and efficiently disperse particles.
The vibratory dispersers have no way of controlling the charge, or lack thereof, of the particles exiting the dispersion system. This can be extremely important for analysis work where the charge of the particle may affect the way the particle is detected by the analysing equipment. In some instances, the static charge remaining on the particles may cause clumping to reoccur almost immediately when the particles exit the system.
It is thus an object of the invention to provide a powder disperser which can quickly and efficiently disperse particles and control the charge of the dispersed particles exiting the system.
Electrostatic energy is a unique force. Harnessing this force has created exciting applications, copying, particle accelerators, dust and smoke precipitators, etc. A new application applies to the field of particle dispersion.
The concept of passing particles through an electrostatic field for the purpose of propelling the particles beyond a screen is disclosed in U.S. Pat. No. 3,635,340 to Dunn. This patent discloses the use of article momentum produced by pulling the particles across a field to propel particles through a printing screen. Further, it is also disclosed that this propulsion of the particles beyond a second electrode may be used for possible particle classification. This patent, however, does not recognize or utilize particle oscillation as the vehicle for dispersion of the particles.